Light affects physiologic parameters, physical growth, sleep-wake states, day/night cycling, and sensory systems of preterm infants. This study will examine the effects of cycled light and continuous near darkness on the growth and development of preterm infants, who will be followed from the time of admission into the neonatal intensive care nursery until term or hospital discharge. Preterm infants less than 31 weeks gestation admitted to a Southeastern regional tertiary care teaching hospital will be eligible for participation. Infants will be randomly assigned to one of 3 groups: Group 1 will receive continuous near darkness from birth until 32 weeks gestation with subsequent cycled light, Group 2 will receive cycled light from birth, and Group 3 will receive continuous near darkness from birth. Outcome measures will include physical growth (height, weight, head circumference), length of hospital stay, number of ventilator days, sleep-wake state organization, day/night organization of physiologic parameters (e.g. heart rate) and neurobehavioral organization (e.g. visual and auditory functioning). The findings are expected to indicate the most appropriate timing of cycled light.